7400 deltaV no enough for a trip to the Mun?

[OptiSTR]

hey guys im having problem with traveling to distant planets...

So im trying to land on the mun the then to fly back home,

I have 7400 DeltaV which is supposed to be enough, yet on my trip back I run out of fuel...

Have anyone have any ideas on why?

I dont do much corrections, I also tried to fly with mechjeb and with same results...

Help :X

[Sir Nahme]

Well I would start with posting in the how to section as that is where such questions should be, but that is more than enough DV for going to and landing on minmus with return so it is either your piloting or a problem with the craft in general.

[Vanamonde]

The figures you see are ideal numbers that assume you didn't do anything wrong, but there are lots of ways to use more fuel than the minimum and run over those numbers. For example, if you descend very slowly to Mun's surface, you will burn a lot of fuel hovering even though you're covering the same distance that the ideal figures talk about. Landing at higher lattitudes on Mun can also cost more fuel than landing near the equator (depending on how you get there), and so on. If you'd like an example, I made a rocket that should have enough dV for the job, and wrote out a flight path that is not ideal, but should be reasonably close to a minimal fuel method. You can find it here: http://forum.kerbalspaceprogram.com/showthread.php/25029-A-moon-rocket-for-newbies

[brooksy125]

Have you tried a more efficient launch profile? (gravity turn, keeping under terminal velocity untill 10k ect)

[rryy]

Your lifter or lander may not have had a large enough TWR. When doing orbital maneuvers, TWR doesn't matter much, but when landing or launching into orbit, a low TWR will burn off a lot of delta-v fighting gravity.

[magnemoe]

7400 might shave it, you use 5000 getting into orbit. 1000 to get to Mun, 400 to get into low orbit and 800 to land.

Not an huge margin of error, upside is that LKO is over halfway to everywhere. If you do the burn right its cheaper to land on Duna than Mun,

[CalculusWarrior]

I tend to split up delta-v assigning into two parts: ascent from orbit, and the Mun mission. So make sure that your lower stages have enough delta-v to get into orbit, and then make sure that your upper stages have enough to get you to the Mun and back.

Ideally, your ascent from ground level to Low Kerbin Orbit should take about 4500-5000 m/s of delta-v. I prefer to engineer a bit of extra safety into my designs and try to aim for the 5000 m/s marker, as it is more forgiving if my Thrust-to-Weight-Ratio is a little lower than optimal, or if I accidently cut my engines halfway through (I have done this). If you can get into orbit, then you're "halfway to anywhere," as a famous man once said.

Then, you can expend the 2500-3000 m/s of delta-v that remains in your upper stage to explore the Mun and return to Kerbin. (I'm assuming you're going with a direct descent Munar lander, rather than have two ships like Apollo).

I would recommend that you build the upper stage first and try to aim for 2.5-3 km/s of delta-v, and the build the lower stage below that and try to get it to 4500 m/s. I've found totals to be a little iffy before, as they don't take into account where you burn your engines (you can get much higher efficiency in space than at sea level, so if you're burning with your transfer stage in atmosphere, then you're wasting fuel).

tl;dr, design your ship in two parts, one to ascend through the atmosphere, the other to get to the Mun and back. If still keep running out of fuel, then at least you'll know where on your spacecraft the excessive fuel consumption is coming from (perhaps your lander, or maybe a capture burn).

I also recommend watching Scott Manley's video tutorial on the subject; it tells you exactly what you have to do to get there and back again:

[Godot]

These are the rough results of my last mission (Apollo Style i.e. Lander + Spaceship)

4500 dV Orbit 100km

800 Burnup to Mun

300 Orbit Mun 50km

Decelerating + Landing 1200

Ascent + Rendezvous with Spaceship 1000

Return to Kerbin 500

Summa: 8300

I might add that my lander with 100 t is rather heavy (concept for my future lander on Duna) and that the landing place wasn´t directly below the orbit of the spaceship, forcing me to burn additional fuel to change the orbital angle of the lander 1. for landing and 2. for ascent+rendezvous again.

All in all the numbers however very well reflect, what Vanamonde already said ... there is a difference between theoretical numbers and practical consumption

Edited June 1, 2013 by Godot

[MBobrik]

check the Delta V map

4500 + 2 * ( 860 + 210 + 640 ) = 7920 m/s bare minimum. I would add at least 500 m/s to the lander and another 200 m/s to the launcher. and x 100 m/s to the moon and back trip. so say 8800 m/s would do it.

[Specialist290]

Strictly speaking, you don't really need to consider that second set of 860 m/s dv fully, since it's much cheaper to return from the Mun than it is to get there (and the atmosphere will kill most of your excess velocity on your reentry approach).

That said, 7400 m/s dv is probably right there on the razor edge. As others have pointed out, the numbers on the delta-v charts assume ideal conditions and perfect piloting, which aren't always the case even with MechJeb helping you.

[SmashingKirby148]

Acording to this map, http://deltavmap.com/

A direct trip to the Mun is 5570 m/s

But a round trip is 11140 m/s. I guessing a round trip is to and back, so you will need more delta V.

[Bloody_looser]

Necro alert.

[Eric S]

As some people have pointed out, the delta-v charts assume fairly optimal maneuvers. The best thing to do would be to measure your delta-v at each point along the trip and let us know which specific steps seem to be costing more delta-v than you calculated they should. Any of the steps could be done inefficiently.

The most common place that you'll find suboptimal maneuvers is in landing. If you go from a normal orbit, kill most of your rotational velocity so that you start dropping, then occasionally thrust upward to keep your downward velocity from getting too high, you can easily double or triple the delta-v required to land, and when I was learning, sometimes I'd go even higher. This is a common way for people to land before they learn how to do it more efficiently.

Some people do rather inefficient launches as well. I normally budget about 4750-4800 m/s for launchpad to LKO, but when I was learning, I'd occasionally have a bad launch that took closer to 6000 m/s delta-v.

The transfer burn should be a single burn in LKO, and should be a hohmann transfer. Don't overshoot, you want the transfer orbit to have an apoapsis very close to the Mun's orbital altitude. If you use a higher apoapsis, then not only does it take more delta-v to transfer into that trajectory, but you have to kill more velocity when you reach the Mun.

Efficient circularization at the Mun requires a fairly accurate intercept. The higher your Munar periapsis pre-circularization, the more delta-v it's going to take to circularize in a low orbit over the Mun. Also note that if you need to lower your periapsis right after crossing into the Mun's SoI, radial burns tend to be more efficient than prograde/retrograde burns in order to change your periapsis, since you're not close to your apoapsis or periapsis.

Returning to Kerbin efficiently is basically burning so that you leave the Mun's SoI moving in the Mun's retrograde direction (compared to the Mun, you'll still be moving in the same direction as the Mun, just not as fast) so that you're in an orbit with an apoapsis near the Mun and a Kerbin periapsis of about 20km. I've never managed to do that perfectly, but you want your munar transfer burn to be as close to this as possible so that any correction burns are small. Lifting so that you're barely out of the Mun's SoI and then setting up the return trajectory may sound close enough, but it's not.

TLDR: Use Kerbal Engineer Redux or MechJeb to measure your delta-v during the mission and compare that to what your plan says you should have, and that should narrow down what part of the mission is going over budget.

Necro alert.

Ugh, sorry.

[Deutherius]

Necro alert.

Not only that, the presented tool is, as of now, kinda broken - it only gives a correct sum of dV for the first body you click on, every other selection fails to reset and gives false results. The map itself is reasonable, though, so if you calculate it yourself, you're going to be good.

Acording to this map, http://deltavmap.com/

A direct trip to the Mun is 5570 m/s

But a round trip is 11140 m/s. I guessing a round trip is to and back, so you will need more delta V.

5570 m/s dV is NOT enough to land on the Mun, btw, you fell victim to the fault described above. You will need at least 6200 m/s just to land (if you're good), and about 800 - 900 m/s dV to return.

[OhioBob]

The numbers that I generally budget for a Mun mission are,

[TABLE=class: outer_border, width: 400]

[TR]

[TD]Launch to Kerbin orbit[/TD]

[TD=align: right]4,550 m/s[/TD]

[/TR]

[TR]

[TD]Injection into trans-Mun trajectory[/TD]

[TD=align: right]860 m/s[/TD]

[/TR]

[TR]

[TD]Mun orbit insertion[/TD]

[TD=align: right]260 m/s[/TD]

[/TR]

[TR]

[TD]Deorbit, descent and landing[/TD]

[TD=align: right]875 m/s[/TD]

[/TR]

[TR]

[TD]Ascent to Mun orbit[/TD]

[TD=align: right]700 m/s[/TD]

[/TR]

[TR]

[TD]Injection into trans-Kerbin trajectory[/TD]

[TD=align: right]270 m/s[/TD]

[/TR]

[TR]

[TD]TOTAL[/TD]

[TD=align: right]7,515 m/s[/TD]

[/TR]

[/TABLE]

As others have said, these numbers can vary depending on how efficiently you perform each maneuver. For example, I'm pretty good at getting to Kerbin orbit, rarely exceeding the 4,550 m/s minimum; however, the technique I use to land on Mun is not the most efficient, though neither is it the least efficient. I use a method that I'm comfortable with and just accept the fact that I must budget a little extra ÃŽâ€v.

[tsotha]

Where did you run out of fuel? Did you almost make it, or are you stuck on the surface of the Mun, unable to make Munar orbit?

[Lohan2008]

MOAR boosters !!

[emerson]

My early career lander has 8600 dV and I land Mun with 1600+ left easy, so about 6000 to get there. Using the dV map I found online it should be 7140 dV to get there and back considering aerobrake to return to Kerbin. (LKO 4500 + 680 Transfer + 180 Mun Transfer + 80 Capture + 230 LMO + 580 Landing + 580 LMO + 230 Escape + 80 Transfer = 7140 minimum)

[mgalyan]

I just rescued some Kerbalnauts I inadvertently stranded on the Mun with 7527 delta V. I barely made it back to Kerbin, and had to use parachutes to land, but it was enough.

[Snark]

This thread is ancient, over three years old.  Not only have any problems mentioned in here presumably long since been overcome, but the game has changed so much in the meantime that any numbers or advice you see here are almost completely irrelevant.

Locking the thread to prevent further confusion.  If you have questions or comments about going to the Mun (or anywhere else), please feel free to spin up a new thread.